1. Field of the Invention
This invention relates generally to a means for calibrating the light-sensitive exposure control system and more particularly to a means for calibrating a light-sensitive exposure control system to insure that the amount of light actually passed by the camera shutter during a photographic exposure interval corresponds to the amount of light required by a select film of a given speed to achieve a satisfactory exposure.
2. Description of the Prior Art
Exposure control systems of the light-responsive type are well known in the art and have been widely used in cameras of all types including those adapted for use with film of the self-developing type. Such exposure control systems generally incorporate a photosensitive transducer to which scene light is directed through a shutter apparatus in correspondence with the scene light directed to the film plane. There is additionally provided a light integrating and control circuit which integrates the signal received from the phototransducer until the signal reaches a predetermined exposure value at which point the control circuit operates to terminate the exposure interval.
Exposure systems of the same design, however, generally operate to provide different exposures resulting from the cumulative effect of variations within prescribed tolerances of the individual electronic components which make up the photocell transducer, and light integrating and control circuitry. Additional variations in the exposure control between identically designed exposure control systems may result from differences between the actual shutter blade dynamics associated with each exposure control system.
In order to eliminate such exposure differences between identically designed exposure control systems, it is often necessary that each exposure control system be individually calibrated to admit precisely that amount of light to the film plane which is required by a particular film of predetermined speed to achieve a correct exposure. Exposure control systems of the light responsive type have been calibrated in the above manner by inserting different neutral density filters, one at a time, into scene light intercepting relation with respect to the scene light directed to the phototransducer. After each filter is inserted, a photographic exposure cycle is completed until the best filter is found which operates to most closely correlate the exposure to a selected film speed. One commercially available camera calibrated in the above described manner is Polaroid Corporation's SX-70 Camera. Calibrating an exposure control system through the use of discrete filters, however, can be a time consuming and expensive operation due to the difficulty associated with physically removing and replacing each discrete filter element subsequent to each exposure calibration cycle. In addition, the variations in light attenuation to the phototransducer depend upon the number of different filters maintained in stock, thus precise calibration may not be possible unless a substantial number of discrete filters having different light attenuating characteristics are kept in stock.
Therefore it is a primary object of this invention to provide a simple and economical means for calibrating a ligh responsive exposure control system for a photographic apparatus.
It is also an object of this invention to provide a simple and economical means for calibrating a light responsive exposure control system so that the light actually admitted by the exposure control system corresponds to the amount of light required by a film of selected speed to achieve correct exposure.
It is a further object of this invention to provide a unitary calibration filter disposed for movement with respect to a light sensitive exposure control system in a manner permitting calibration of the exposure control system without the use of a plurality of individual discrete filter elements as heretofore required.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.